The present invention relates to a bidirectional communication line buffer apparatus provided on a bidirectional communication line used for connecting appliances.
FIG. 8 is a block diagram showing a conventional bidirectional communication line used for connecting appliances.
In FIG. 8, the reference numerals 1 and 2 designate a first control portion and a second control portion which are provided in a first appliance and a second appliance respectively. The first and second control portions are connected through a plurality of bidirectional communication lines, such as, for example, a serial clock line 3.sub.1, a data line 3.sub.2, a reset line 3.sub.3, . . .
Next, the operation of the conventional system of FIG. 8 will be described.
In the case of data to be transmitted from the first control portion 1 to the second control portion 2, when the first control portion 1 sends out serial clock signals and data signals onto the serial clock line 3.sub.1 and the data line 3.sub.2 respectively, the second control portion 2 judges the state of the data signals received on the data line 3.sub.2 on the basis of the serial clock signals received on the serial clock line 3.sub.1 to thereby receive the data signals transmitted from the first control portion 1.
For example, upon reception of a transmission termination data signal inserted in the data at its last portion, the second control portion 2 terminates the data reception from the first control portion 1.
The same applies to the case where data is to be transmitted from the second control portion 2 to the first control portion 1.
Thus, the conventional appliances are connected through one system of a plurality of lines 3.sub.1, 3.sub.2, 3.sub.3, . . . Accordingly, when the scale of the whole system is small, the number of control portions is also small as shown in FIG. 8 so that the total length of the respective lines 3.sub.1, 3.sub.2, 3.sub.3, . . . of the data transmitting-end control portion and the data receiving-end control portion is short and the transmitting pulse waveform is never distorted, thereby permitting data to be transmitted accurately.
As the scale of the system becomes large, however, the number of control portions correspondingly increases so that the total length of the respective lines 3.sub.1, 3.sub.2, 3.sub.3, . . . of the data transmitting-end control portion and the data receiving-end control portion becomes long even if the length of each of the lines 3.sub.1, 3.sub.2, 3.sub.3, . . . is fixed so that the transmitting pulse waveform becomes distorted.
When the distortion of the transmitting pulse waveform becomes excessive, there results an error situation in the data transmission process.
A buffer apparatus can be used for amplifying a pulse waveform in the midway of each of the lines 3.sub.1, 3.sub.2, 3.sub.3, . . . Since each of the lines 3.sub.1, 3.sub.2, 3.sub.3, . . . is a bidirectional communication line, however, it is necessary to drive the buffer apparatus on the basis of a judgement of the communication direction of data. Accordingly, the configuration becomes complicated because of the necessity of driving the buffer apparatus in accordance with the communication direction.